Power control circuit testing involves timing when a load is applied to, or removed from, a circuit. One method used to perform this monitoring is to monitor the voltage at a load output. Typically, in order to monitor an AC output, a peak detector is used. Peak detectors rectify and filter the AC output and sense the resulting voltage levels to determine if a load is being driven by an AC power source.
An AC voltage being applied to the load is detected when the output voltage of the peak detector crosses from below an upper detection threshold to above the upper detection threshold. A capacitor in the detection circuit then holds the voltage between peaks for ½ cycle of the input AC waveform above the upper detection threshold in order to prevent false load state changed events. A load detection circuit using a capacitor in this manner is to be referred to as a capacitive hold AC voltage detector.
When a load is removed from the circuit, the capacitor slowly discharges and the removal of the load is detected when the voltage falls below a lower detector threshold. The slow discharge is due to the presence of the capacitor and relatively the large capacitance values that must be used to prevent false output changes when AC power is applied or removed from the monitored load.